A motor refers to an apparatus that uses a principle that a force is produced in a direction perpendicular to magnetic flux produced from a permanent magnet and electric current flowing through a conductor when the magnetic flux is perpendicular to a direction of the electric current, and converts this force into a rotational force.
This motor generally includes windings that are conductors conducting electricity, a stator including permanent magnets, a rotor converting electric energy supplied to the stator into mechanical energy, a shaft serving to support the rotor, and a bearing allowing the rotor and the shaft to be smoothly and constantly rotated.
This motor may be classified as a radial flux motor or an axial flux motor on the basis of a direction of the magnetic flux emitted from the permanent magnets.
The radial flux motor is configured so that permanent magnets mounted in a radial direction serves as the rotor, and windings for producing a magnetic field in a radial direction and a core to which a magnetic force from the permanent magnets is applied serve as the stator. With this configuration, the magnetic field produced by interaction of the permanent magnets and the windings is transmitted to the core so as to be able to generate a rotational force. This radial flux motor may be provided with a pulling plate in order to produce a preload for supporting the shaft on the bearing.
In contrast, the axial flux motor is configured so that windings producing a magnetic force in an axial direction are fixed to the stator and permanent magnets mounted in the axial direction are fixed to the rotor. A rotational force can be produced by interaction of the windings and the permanent magnets.
In the case of the aforementioned radial flux motor, since the permanent magnets are mounted so as to produce the magnetic field only in the radial direction, there is a limitation that an axial magnetic force is weak, and thus an axial preload is required for the bearing in order to axially support the rotor that is rotated. In contrast, in the axial flux motor, there is a disadvantage in that a greater axial magnetic force than needed is produced due to the permanent magnets mounted in the axial direction.